1. Field of the Invention
The present invention relates to voltage regulating circuits, and particularly to a voltage regulating circuit for a motherboard.
2. Description of related art
A typical microprocessor-cored computer system, such as a personal computer or a workstation computer, is turned on and off by a switch device that mechanically connects/disconnects a power supply of the computer system to/from an external voltage source, such as AC 110V. The power supply is connected to the external voltage source and transforms the external voltage into a predetermined DC level, such as +3.3V, +/−5V and +/−12V, and the computer system is turned on to perform various programs and functions.
As known by a person skilled with computers, the power supply mainly includes ATX power supply and BTX power supply. A motherboard of a computer can be coupled to the ATX power supply via a 20-pin ATX power connector and two 4-pin ATX power connectors. The ATX power supply provides +3.3V, +/−5V, +/−12V, +5V_SB (stand by), PS_ON (power supply on) signal, and PWR_DOOD (power good) signal. When the ATX power supply is turned on, the PS_ON signal is at a low level, and the PWR_GOOD signal is at a high level but there is a delay of 100-500 ms for the other voltages. When the ATX power supply is turned off or put on stand by, the PS_ON signal is at a high level, and +3.3V, +/−5V, +/−12V are turned off, but the +5V_SB is still provided.